This invention relates to an extrusion apparatus, particularly to an extrusion apparatus having a modified preland channel.
As illustrated by U.S. Pat. Nos. 4,789,513 and 4,780,258, both to Peter F. Cloeren, a coextrusion apparatus including a removable die body with a coat hanger-type manifold and a conventional preland channel for producing substantially equal flow volume of a stream across the stream width, is known. Also known as exemplified by U.S. Pat. No. 4,600,550 to Peter Cloeren, is an extrusion apparatus having a restriction channel of increasing cross-sectional area from the center thereof to each end thereof, for causing a stream to flow at substantially equal pressure from side to side; however, effectiveness could be improved.
An interchangeable insert for modifying flow volume, would permit insert selection based upon for instance, stream rheology and in the case of a multimanifoId extrusion die, also based upon the desired relative layer thickness of a composite. Rigid mounting of the insert would provide a fixed geometry to converging channels.
Therefore, there is a need for an improved extrusion apparatus that is effective in providing for substantially equal flow volume of a stream across the stream width. Beneficially, such an apparatus would include an interchangeable insert or inserts for enabling this result.